Try a 10w-30, sample if you're concerned and make a decision from there. I do tow and haul weight every day in my 6.7. I, however, never see over 5% bio as my fuel supply is delivered here, I rarely buy fuel on the road, maybe twice a year. I also used 10w30 in my previous 6.0, without issue.
I'm aware of what the owners manual states and I've always had better UOA results with 10w-30 vs. 5w40, go figure. Everyones duty cycle is different, evidently what I'm using the truck for is easy on the engine. My suggestion is 10w-30, just because you're towing doesn't automatically mean you're severe duty, where are your oil temps at while towing? I recently towed a 12,000 GVW trailer (loaded) 140 mi. and never saw oil temps exceed 214f. I haven't concerned myself with using 10w-30 in one of my trucks for years as the UOA data has proven to me zero issues.